System for and method of providing a header and a trailer in data packets

ABSTRACT

Each packet normally consists of a preamble, start-of-frame delimiter and data. The preamble has nibbles each having a particular format. A header substituted for preamble nibbles by an individual one of the originating devices in a plurality, and an individual one of the ports in such originating device, indicates such originating device and such port. Such port in such originating device sends such modified packet to others of the originating devices and to an observing station. The header format is such that the last nibble in the header and the remaining preamble portion will not be confused with any two (2) nibbles in the header. A particular one of the originating devices indicated in the data converts the header back to the preamble format and transmits the converted packet to a receiving station. The observing station records the individual originating device, and the individual port in such device, indicated in the header. Each packet includes at its end a trailer formed from a plurality of nibbles and indicating whether or not a collision has occurred between such packet and a packet from another one of the originating devices. The trailer in each packet may also indicate additional information—e.g. whether the packet (a) is a normal packet originally formed, (b) is a runt packet, (c) is from an unacceptable source and (d) the delay between each packet end and the next packet start. The information in the trailer for each packet passes to the observing station.

[0001] This invention relates to a system for, and method of, providinga header for indicating to an observing station an individual one of aplurality of originating devices, and an individual one of the ports insuch originating device, providing packets of data. The invention alsorelates to a system for, and a method of, providing a trailer forindicating whether a collision has occurred between the transmission ofpackets from such individual one of the ports in such individual one ofthe originating devices and packets from another one of the originatingdevices.

BACKGROUND OF THE INVENTION

[0002] Systems are provided for transmitting data in packets. Eachpacket may have at least a particular length (e.g. at least 512 nibbles)where each nibble consists of a plurality (e.g. four (4)) binary bits.Each packet may include a preamble, a start-of-frame delimiter and data.The preamble in each packet is provided to synchronize the subsequentnibbles in the packet with clock signals. The preamble may consist of aplurality of nibbles each having the same particular format. Thestart-of-frame delimiter includes a plurality of nibbles indicating thatdata follows such delimiter. In addition to providing information, thedata may include an identification of the source of the packet and therecipient of the packet.

[0003] It is sometimes desired to make a record of the individual one ofthe originating devices, and the individual one of the ports in suchoriginating device, providing the packets. Two (2) different approacheshave been provided in the prior art to record such information. Oneapproach has been to provide additional signal lines to record theindividual one of the originating devices, and the individual one of theports in such originating device, providing the packets. The use of suchadditional signal lines is not satisfactory because it undulycomplicates the construction of the system. A second approach has beento provide a trailer at the end of the packet to indicate the individualone of the originating devices and the individual one of the ports insuch originating device. This is not desirable because it shortens thespace between successive packets.

[0004] Sometimes two (2) originating devices transmit packets at thesame time. This causes a collision to occur between the two (2) packets.Any other originating device simultaneously receiving the two (2)packets will become confused and accordingly generate wrong information.It is desirable to record the occurrence of such a collision. It is alsodesirable to record other information upon the occurrence of acollision. This would include the spacing between successive packets andindications of a normal packet or variations from a normal packet. Noone until now has used the same lines normally used for passing thepacket in order to record the occurrence of collisions, the spacingbetween packets and indications for each packet that the packet isnormal or varies in specified ways from a normal packet.

BRIEF DESCRIPTION OF THE INVENTION

[0005] This invention provides a system for, and method of, providingand recording the different information specified *above. For example,the system and method of this invention provide such information in arelatively straightforward manner without complicating the constructionof the system. The system and method of this invention illustrativelyprovide for a recording of the individual one of the originating devicesin a plurality, and the individual one of the ports in such originatingdevice, providing packets of information. The system and method of thisinvention also provide for the determination of collisions betweenpackets simultaneously transmitted from two (2) of the originatingdevices in the plurality and for the indication of the occurrence ofsuch collisions.

[0006] In one embodiment of the invention, each packet normally consistsof a preamble, a start-of-frame delimiter and data. The preamble hasnibbles each having a particular format. A header substituted forpreamble nibbles by an individual one of the originating devices in aplurality, and an individual one of the ports in such originatingdevice, indicates such device and such port in such originating device.Such port in such originating device sends such modified packet toothers of the originating devices and to an observing station.

[0007] The header format is such that the last nibble in the header andthe remaining preamble portion will not be confused with any two (2)nibbles in the header. A particular one of the originating devicesindicated in the data converts the header back to the preamble formatand transmits the converted packet to a receiving station. The observingstation records the originating device, and the port in such device,indicated in the header.

[0008] Each packet includes at its end a trailer formed from a pluralityof nibbles and indicating whether or not a collision has occurredbetween such packet and a packet from another one of the originatingdevices. The trailer in each packet may also indicate additionalinformation—e.g. whether the packet (a) is a normal packet, (b) is arunt packet, (c) is from an unacceptable source and (d) the delaybetween each packet end and the next packet start. The information inthe trailer for each packet passes to the observing station.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a diagram showing the different portions of aninformation packet normally transmitted in the prior art;

[0010]FIG. 2 is a diagram showing the different portions of aninformation packet modified in accordance with the concepts of thisinvention, such different portions including a header for indicating anindividual one of a plurality of originating devices, and an individualone of the ports in such originating device, sending such packet;

[0011]FIG. 3 is a table showing how the header indicates the individualone of the plurality of originating devices and the individual one ofthe ports in such originating device;

[0012]FIG. 4 is a diagram, similar to that shown in FIGS. 1 and 2, ofthe different portions of a packet and includes a header and alsoincludes a trailer at the end of the packet for indicating theoccurrence of a collision resulting from a simultaneous transmission ofpackets from two (2) of the originating devices in the plurality andalso includes a waveform showing the transmission of the signals in thepacket when no collision occurs;

[0013]FIG. 5 is a table similar to that shown in FIG. 3 and shows howthe trailer in the packet indicates a lack of a collision betweenpackets and also indicates other specific data;

[0014]FIG. 6 is a table showing how different data other than theoccurrence or lack of occurrence of a collision are indicated in thetable shown in FIG. 5;

[0015]FIG. 7 is a diagram, similar to that shown in FIG. 4, of a packetwith a header and a trailer and shows the signal waveform produced inthe packet upon a lack of occurrence of a collision between this packetand another packet and additionally shows the signal waveform producedin the packet upon the occurrence of a collision;

[0016]FIG. 8 is a table showing the pattern of signals produced in thetrailer in a packet when there is a collision between this packet andthe simultaneous transmission of another packet;

[0017]FIG. 9 is a block diagram of circuitry for detecting collisionsbetween packets simultaneously transmitted by a pair of originatingdevices;

[0018]FIG. 10 is a schematic circuit diagram showing in block form aplurality of originating devices on a pair of printed circuit boards forreceiving and transmitting packets of information and further showing anobserving station on another printed circuit board for recording theinformation in the headers of packets transmitted by an individual oneof the originating devices and by an individual one of the ports in suchoriginating device;

[0019]FIG. 11 is a circuit diagram showing in additional detail a pairof the originating devices shown in FIG. 10 and also showing inadditional detail the circuit interrelationships between the originatingdevices and the observing station;

[0020]FIG. 12 is a detailed circuit diagram in block form of one of thedata multiplexers shown as a single block in the circuit diagram of FIG.11;

[0021]FIG. 13 is a detailed circuit diagram in block form of anexpansion controller and arbiter shown as a single block in the circuitdiagram of FIG. 11;

[0022]FIG. 14 is a detailed circuit diagram in block form of anexpansion state machine shown as a single block in the circuit diagramof FIG. 13;

[0023]FIG. 15 is a circuit diagram in block form and shows in additionaldetail a data forwarding stage shown as a single block in FIG. 11;

[0024]FIG. 16 is a detailed circuit diagram in block form of astart-of-frame detect stage shown as a single block in FIG. 15;

[0025]FIG. 17 is a detailed circuit diagram in block form of a dataprocessor shown as a single block in FIG. 11;

[0026]FIG. 18 is a detailed circuit diagram in block form of a dataprocessing state machine shown as a single block in FIG. 17;

[0027]FIG. 19 is a table specifying the definitions of various termsused in the previous figures; and

[0028]FIG. 20 shows voltage wave forms at strategic terminals incircuitry included in some of the previous Figures.

DETAILED DESCRIPTION OF THE INVENTION

[0029]FIG. 1 is a schematic view of an information packet, generallyindicated at 10, normally provided in the prior art. The packet isformed from a plurality of nibbles each formed from a plurality ofbinary bits. For example, each nibble may be illustratively formed fromfour (4) binary bits which may be provided in a parallel relationship.The packet 10 may be provided with an idle portion 12, a preamble 14, astart-of-frame delimiter 16, data 18 and a trailer 20.

[0030] The preamble 14 is provided at the beginning of the packet 10 tosynchronize the presentation of the successive nibbles in the packetwith a clock signal. Each nibble 14 in the preamble may have the sameformat as the other nibbles in the preamble. For example, each nibble inthe preamble may indicate an analog value of “5” in hexadecimal codedform.

[0031] The start-of-frame delimiter 16 indicates the beginning of thedata portion 18 of the packet 10. It is provided in a particularpattern. It is followed by the data portion 18 of the packet 10. Thedata portion 18 provides the information in the packet. It may alsoindicate the source from which the packet 10 is provided. It mayadditionally indicate the station which is to receive the packet.

[0032] In one embodiment of the invention, a plurality of integratedcircuit boards generally indicated at 24 and 26 in FIG. 10 may beprovided. Although only two (2) boards 24 and 26 are shown in FIG. 10,it will be appreciated that a considerably greater number of boards thantwo (2) may be provided.

[0033] Each of the boards such as the boards 24 and 26 may have asubstantially identical construction. Each of the boards 24 and 26 mayinclude a plurality of integrated circuit chips 30. Each of the chips 30may have a substantially identical construction. For example, each ofthe chips 30 may constitute a 5205 chip developed by, and fabricatedfor, applicant's assignee of record in this application.

[0034] Each of the chips 30 may be considered to constitute anoriginating device. The cumulative number of originating devices 30 onthe boards 24 and 26 may be considered to constitute a plurality. Eachof the originating devices 30 has a plurality of ports 32. The packets10 pass into an individual one of the originating devices 30 through anindividual one of the plurality of ports 32 in such individual one ofthe originating devices.

[0035] As previously described, the packets 10 include the trailer 20 inone form of the prior art shown in FIG. 1. The trailer 20 indicates anindividual one 30 a of the originating devices 30 and the individual one(e.g. 32 b) of the ports 32 for passing the packets from suchoriginating device. The packets 10 pass to an observing station 34 whichrecords the individual one 30 a of the originating devices 30, and theindividual one (e.g. 32 b) of the ports 32 in the originating device 30a, through which the packets pass. As will be appreciated, it would bebetter not to provide the trailer 20 at the end of the packets 10 torecord the originating device 30 a and the port 32 b because thisconstitutes an inefficient use of the space between successive packets.

[0036]FIG. 2 shows packets generally indicated at 40. The packets 40have been modified by applicants from the packets 10 of the prior art toobtain the advantages of this invention. As will be seen, the packets 40are substantially identical to the packets 10 except that theysubstitute a header 42 for a portion of the preamble 14. Furthermore, atrailer 44 is included at the end of the packets 40 but the trailer 44provides completely different functions than the trailer 20 in thepackets 10 and provides these different functions on a more efficientbasis than in the prior art. This will be described in detailsubsequently.

[0037] The header 42 may be formed from four (4) nibbles respectivelydesignated as H1, H2, H3 and H4. They constitute substitutions for thefirst four (4) nibbles in the preamble 14 in the packets 10. The nibblesH1, H2, H3 and H4 are not used to provide a synchronization with theclock signals. They are used to indicate the originating device 30 a,and the port 32 b in the originating device 30 a, through which thepackets 40 pass.

[0038]FIG. 3 is a table indicating the format of the header 42 formed bythe nibbles H1, H2, H3 and H4. As will be seen, each of the nibbles H1,H2, H3 and H4 may illustratively be formed from four (4) binary bits. Itwill be appreciated that a different number of bits than four (4) may beused to define each nibble without departing from the scope of theinvention. Six (6) of the binary bits in the table are respectivelydesignated as “PG15”, “PG14”, “PG13”, “PG12”, “PG11” and “PG10”. Theseindicate an individual one of sixty-four (64) different originatingdevices 30. Four (4) of the binary bits in the table are respectivelydesignated as “PID3”, “PID2”, “PID1” and “PID0”. These indicate anindividual one of sixteen (16) possible different ports in theindividual one of the originating devices represented by thedesignations “PG15”-“PG10”.

[0039] It is desirable that the four (4) binary bits in the nibble H4and in the first nibble in the remaining portion of the preamble 14 havea pattern different from the binary bits in any two (2) successivenibbles in the start-of-frame delimiter 16. This prevents any confusionfrom arising between the header and the preamble in the packet 40 on theone hand and the start-of-frame delimiter in such packet on the otherhand when the information in the packet 40 is processed. It is alsodesirable that the last nibble in the header and the remaining preambleportion will not be confused with any two (2) nibbles in the header.

[0040] As indicated previously, the packets 40 pass from the originatingdevice 30 a to all of the other originating devices 30 in the plurality.The packets 40 may pass through an originating device 30 b in accordancewith the instructions from the external source (not shown). However,before the packets 40 pass through the originating device 30 b, theheader 42 represented by the nibbles H1, H2, H3 and H4 is converted inthe originating device 30 b to the particular pattern in the preamble14.

[0041] The packets 40 also pass to the printed circuit board 34. Theprinted circuit board 34 may be considered to provide an observingstation. It includes an integrated circuit chip designated as the 5205by applicants' assignee of record in this application and developed by,and fabricated for, such assignee. The observing station 34 processesthe information in the header 42 and, from such processing, determinesthe identity of the originating device 30 a, and the individual one ofthe ports 32 b in such originating device, through which the packets 40pass. The observing station 34 then records, in a memory 52 indicated as“statistics” in FIG. 17, the identity of the originating device 30 a andthe individual one of the ports 32 b in such originating device. Theobserving station 34 also detects and records whether any informalities(e.g., the delimiter) are missing from the packet.

[0042] The trailer 44 in the packets 40 provides a different functionthan the trailer 20 in the packets 10. As shown in FIGS. 4 and 20, anexpansion data valid (XDV) signal 60 is produced at the beginning of theheader 42 in the packets 40. The expansion data valid signal 60 thencontinues until the end of the data 18. When there is no collision as aresult of a simultaneous transmission of packets from the originatingdevice 30 a and another one of the originating devices 30, the XDVsignal is negated during the production of the trailer 18 represented bythe nibbles T1, T2, T3 and T4. The failure to produce a collision can beseen from FIG. 4 in the line designated as “XDV” since no signal isproduced during the nibbles T1, T2, T3 and T4.

[0043]FIG. 5 provides a table showing the signals which are producedduring the nibbles T1, T2, T3 and T4 when there is no collision betweena packet from the originating device 30 a and a packet from another oneof the originating devices 30. In this table, the successivedesignations “IPG5” to “IPG0” indicate the gap between successive pairsof the packets 40 from the originating device 30 a.

[0044] In FIG. 5, four (4) nibbles “CS3-CS30” are provided. Thesenibbles provide a check sum to indicate whether the nibbles H1-H4 andthe nibbles T2 and T3 constitute proper indications. These nibbles haveproper indications when the values provided in these nibblescumulatively have a particular value. This is well known in the priorart.

[0045] The designations “EV1” and “EV0” in the table shown in FIG. 6 arecombined to provide several different indications which representseveral different special situations. Illustrative examples of thesespecial situations are shown in FIG. 6 and discussed below but otherexamples of these special situations may be provided without departingfrom the scope of the invention.

[0046] When the binary bits EV1 and EV0 in FIG. 6 are both zero (0), anormal packet such as indicated at 40 may illustratively be provided.When the binary bit EV1 is 0 and the binary bit EV0 is 1, a runt frameor packet may illustratively be indicated. A packet generally consistsof at least 128 nibbles. When the number of nibbles in the packet 40 isless than 128, a runt frame or packet is indicated. A runt frame orpacket is generally not processed. However, sometimes a runt frame orpacket is sent to a separate receiver to control internal features inthe receiver. The runt frame or packet then instructs that receiver howto handle certain calls to that receiver.

[0047] A binary value of 1 for EV1 and a binary value of 0 for EV0 inFIG. 6 may illustratively indicate to the observing station 34 that thepacket being received at the observing station is from an unacceptablesource. Binary values of 1 for each of EV1 and EV0 may illustrativelyindicate that the packet 40 is malformed. For example, the packet 40 maybe missing the start-of-frame delimiter 16.

[0048] The table shown in FIG. 5 includes a column designated as “XERR”.This column indicates whether there is a collision as a result of asimultaneous transmission of packets by the originating device 30 a andby another of the originating devices 30. As will be seen, there is a“0” indication in the column XERR in FIG. 5 for each of the nibbles T1,T2, T3 and T4. This indicates that no collision has occurred.

[0049]FIG. 7 is similar to FIG. 4 except that it indicates a collisionbetween the packet 40 from the originating device 30 a and a packet fromone of the other originating devices 30. This may be seen by theproduction of a collision signal 70, in the column designated as XERR inFIG. 7, during the production of the nibbles T2, T3 and T4. In the tableshown in FIG. 8, the column designated as “XD” actually corresponds tothe columns XD3, XD2, XD1 and XD0 in the table shown in FIG. 5.

[0050] When a collision occurs, all of the values in the columns XD3,XD2, XD1 and XD0 become zero since the transmission of packets becomeshalted in midstream when a collision occurs. In this way, only acollision indication is provided in the nibbles T1, T2, T3 and T4 when acollision occurs. This is indicated by a binary “0” in the nibble T1 andby a binary “1” in each of the nibbles T2, T3 and T4. A binary “0” isprovided in the nibble T1 in the XERR column to maintain compatibilitywith the first nibble for a normal trailer.

[0051]FIG. 9 is a circuit diagram schematically illustrated at 80 andshowing a system for indicating how two (2) originating devices 30 a and30 c operate to indicate a collision between packets simultaneouslytransmitted by such originating devices. The system 80 indicates anexpansion bus 82 for passing the XDV and XERR signals (also shown inFIG. 8) and the XCLK and XDATA signals between the originating devices30 a and 30 c. XCRSOUT signals respectively pass from the originatingdevices 30 a and 30 c through lines 84 a and 84 b to “or” networks 86 aand 86 b.

[0052] The XCRSOUT signals on the lines 84 a and 84 b indicate that anindividual one of the originating devices 30 a and 30 c is about totransmit a packet. The XCRSOUT signal on one of the lines 84 a and 84 bindicates to the other originating devices 30 (including the originatingdevice 30 c) that one of the originating devices (e.g. 30 a) is about totransmit a packet. The XCRSOUT signal from the originating device 30 apasses through the “or” networks 86 a and 86 b and XCRSIN lines 88 a and88 b to the originating devices 30 a and 30 c to indicate to suchoriginating devices that the originating device 30 a is about to send apacket.

[0053] The XCRSOUT signal is indicated at 90 in FIG. 20. The XCRSOUTsignal 90 is generated by a clock on one of the printed circuit boards(e.g. the board 24). This clock is different from the clock (XCLK) onthe expansion bus 82. The XCLK signal is indicated at 92 in FIG. 20.Because of this, the XCRSOUT signal can be generated before thegeneration of the XCLK signals 92. An XDIR_(—)0 signal 94 is generated aparticular period of time after the generation of the XCRSOUT signal 90.The difference in time between the initiation in the generation of theXCRSOUT signal 90 and the XDIR_(—)0 signal 94 may be considered toconstitute a Collision Resolution Time. This difference in time isindicated at 95 in FIG. 20. The Collision Resolution Time is provided toallow other originating devices than the originating device 30 a time toindicate to the originating device 30 a that at least one of such otheroriginating devices will be transmitting a packet simultaneously withthe transmission of a packet by the originating device 30 a.

[0054]FIG. 9 also shows XCOLOUT signals respectively passing throughlines 96 a and 96 b from the originating devices 30 a and 30 c to acollision detect stage 98. The XCOLOUT signals indicate a collision as aresult of a simultaneous transmission of packets by two originatingdevices such as the originating devices 30 a and 30 c. XCOLIN signalsrespectively pass from the collision detect stage 98 through lines 99 aand 99 b to the originating devices 30 a and 30 c. The XCOLIN signalsindicate to the originating devices 30 a and 30 c that a collision hasoccurred as a result of the simultaneous transmission of packets by suchoriginating devices. As will be seen, the XCOLIN signals indicate to allof the originating devices 30 on the printed circuit boards 24 and 26that a collision has occurred.

[0055] When the Collision Resolution Time 95 in FIG. 20 has expiredwithout the occurrence of an XCOLIN signal, the originating device 30 astarts to drive the expansion bus 82 in FIG. 9 in providing data fortransmission to the other originating devices including the originatingdevice 30 c in FIG. 10 as discussed above. This occurs when the XCLKline starts to provide clock signals as indicated at 92 in FIG. 20 andwhen the originating device 30 a provides a data valid signal asindicated at 60 in FIGS. 4 and 20. The originating device then providesthe header 42, the remainder of the preamble 14, the start-of-framedelimiter 16, the data 20 and the trailer 44 to the expansion bus 82.This is indicated at 104 in FIG. 20. If the XCOLIN signal is asserted bythe collision detect stage 98 at any time prior to the expiration of theCollision Resolution Time (95 in FIG. 20), the expansion bus 82 remainsundriven for the remainder of the packet from the originating device 30a.

[0056] It may sometimes happen that the XCOLIN signal is detected afterthe Collision Resolution Time has expired. When this occurs, theoriginating device 30 a driving the expansion bus 82 generates acollision trailer as indicated at 70 in FIGS. 7 and 20 and discontinuesany driving of the expansion bus 82. As will be seen at 70 in FIG. 20,the collision trailer 70 is generated as soon as a collision is detectedas a result of a simultaneous transmission of packets by the originatingdevice 30 a and one of the other originating devices 30.

[0057] A broken oval is indicated at 100 in FIG. 9 for the originatingdevice 30 a. This broken oval encloses the line 88 a (XCRSIN), the line84 a (XCRSOUT), the line 96 a (XCOLOUT) and the line 99 a (XCOLIN). Thisbroken oval also encloses the portion of the originating device 30 areceiving signals on the lines 88 a, 84 a, 96 a and 99 a. The portion ofthe system within the broken oval 100 is designated as “ArbitrationInterface.” It indicates the portion of the circuitry shown in FIG. 9that arbitrates whether a collision has or has not occurred.

[0058] One key to the backplane arbitration system shown in FIG. 9 anddescribed above is the Collision Resolution Time. The duration of thistime is set to be greater than the time required for the collisiondetect block 98 to signal XCOLIN to the originating devices 30 a and 30c in the worst case in the operation of the system. If the algorithm forproviding a collision detect signal requires a time greater than theCollision Resolution Time, multiple ones of the originating devices 30will be able to drive the expansion bus 82 simultaneously, therebydestroying the signal integrity of the bus.

[0059] In applicant's embodiment of the invention, the observing station34 in FIG. 10 does not maintain a record of collisions because thetrailer nibbles T1-T4 indicate that a collision has occurred. It will beappreciated, however, that it is within the scope of the invention forthe observing station 34 to indicate the occurrence of a collision. Atany rate, the trailer nibbles T1-T4 distinguish to the observing station34 between a collision and a runt frame or packet. In this way, theobserving station 30 records only a runt frame or packet and does notrecord a shortened packet resulting from a collision. Furthermore, theoriginating device 30 a indicates a collision when the collision hasoccurred between a packet from the originating device 30 a and one ofthe other originating devices 30 in the system.

[0060]FIG. 11 is a schematic circuit diagram of an expansion bus systemwhich includes the originating devices 30 a and 30 c and includes theobserving station 34. The expansion bus 82 (also shown in FIGS. 9 and10) is divided into two (2) segments, one indicated at 82 a and theother indicated at 82 b. The expansion bus 82 a provides informationrelating to the data valid (xdv) signal 60 in FIGS. 4 and 20, the clock(XCLK) 92 in FIG. 20 and the collision (XERR) signal 70 in FIGS. 7 and20. The expansion bus 82 b provides the xdata signals indicated at 104in FIG. 20. As will be seen, each of the expansion buses 82 a and 82 binterconnects the originating devices 30 a and 30 c and the observingstation 34. This interrelationship is known in the prior art and is notaffected in any way by the system or method of this invention. This isone of the advantages of the system of this invention.

[0061] Each of the originating devices 30 a and 30 c in FIG. 11 includesan expansion controller and arbitration stage 104, a data multiplexer(MUX) 106 and a data forwarding stage 108. The expansion controller andarbitration stage 104 provides much of the functions shown in FIG. 9 anddescribed above in connection with FIG. 9. The data multiplexer 106provides for a controlled passage of the header nibbles (H1-H4) and thetrailer nibbles (T1-T4). The data forwarding stage 108 provides for acontrolled transfer of the nibbles representing the data in each packet.The stages 104, 106 and 108 are shown in detail in subsequent Figuresand additional discussion relating to these stages will be providedsubsequently in connection with these Figures.

[0062] The observing station 34 includes a data processor 110 forproviding a controlled passage of the nibbles H1-H4 representing theheader and the nibbles T1-T4 representing the trailer. The dataprocessor 110 is shown in additional detail in FIGS. 17 and 18.Additional discussion relating to the data processor 110 will beprovided in connection with these Figures.

[0063] The expansion controller and arbitration stages 104 in theoriginating devices 30 a and 30 c receive a data valid signal on lines112 a and 112 b. This data valid signal is indicated at 60 in FIGS. 4, 7and 20. The stages 104 in the originating devices 30 a and 30 crespectively provide the XCRSOUT signals (also shown in FIG. 9) on thelines 84 a and 84 b to the carrier and collision detect stage 114 andrespectively provide the XCOLOUT signals (also shown in FIG. 9) on thelines 96 a and 96 b to the collision detect stage.

[0064] The collision detect stage 114 in FIG. 11 respectively passes theXCRSIN signals on the lines 88 a and 88 b, and the XCOLIN signals (alsoshown in FIG. 9) on the lines 99 a and 99 b, to the data forwardingstage 104 in the originating devices 30 a and 30 c. The datamultiplexers 106 in the originating devices 30 a and 30 c in FIG. 11respectively receive data (rxData) on lines 116 a and 116 b. The dataforwarding stages 106 in the originating devices 30 a and 30 crespectively transmit data (txData) on lines 118 a and 118 b.

[0065] The data multiplexer (MUX) 106 (FIG. 11) is shown in additionaldetail in FIG. 12. It includes a plurality of multiplexers 120 a-120 i.The multiplexer 120 a has two (2) inputs, one constituting an “idle” andthe other constituting received data (rxData). The passage of one or theother of these inputs through the multiplexer 120 a is controlled by asignal on a dataSelect (idle) line 122 a.

[0066] Each of the multiplexers 120 b-120 i respectively has a firstinput from the output of the previous stage. Each of the multiplexers120 b-120 i respectively has a second input from an individual one oflines 124 b-124 i. The lines 124 b-124 e are respectively designated ashdr1-hdr4. They provide the header nibbles H1-H4. The lines 124 f-124 iare respectively designated as trlr1-trlr4. They provide the trailernibbles T1-T4. The operation of each of the multiplexers 122 b-122 i isrespectively controlled by an individual one of control lines 122 b-122i. The control lines 122 b-122 e are respectively designated asdataSelect(hdr1) dataSelect(hdr4)). The control lines 122 f-122 i arerespectively designated as dataSelect(trlr1) dataSelect(trlr4).

[0067] The operation of the multiplexer 106 in FIG. 12 may be seen fromthe following examples. When the dataSelect(hdr1) signal on the line 122b is a binary 1, the hdr1 signal on the line 124 b passes through themultiplexer 120 b. The hdr1 signal actually constitutes the H1 nibble inthe header. Since the hdr1 signal is a nibble, a data multiplexercorresponding to the multiplexer 120 b would be provided for each of thefour (4) binary bits in the header nibble H1. When the dataSelect(hdr1)signal is a binary 0, the output signal from the multiplexer 120 apasses through the multiplexer 120 b. Thus, if all of the data Selectsignals on the lines 122 b-122 i constitute binary O's, the receiveddata (rxData) introduced to the multiplexer 120 a passes through all ofthe multiplexers to a line 126 constituting the output of themultiplexer 120 i. The data on the line 126 is designated as xdata. Inthis way the originating device 30 a either passes the received data(rxdata) or substitutes header nibbles H1-H4 for the first four (4)nibbles of the preamble and provides the four additional nibbles T1-T4for the trailer.

[0068] The expansion controller and arbitration stage 104 in FIG. 11 isshown in additional detail in FIG. 13. It includes collision logic 130,an expansion state machine 132, a collision timer 134 and interfacelogic 136. The collision logic 130 receives the XCOLIN signal on theline 99 a (see also FIGS. 9 and 11) and introduces a collision signal ona line 138 to the expansion state machine 132. The expansion statemachine 132 also has an input from the received data valid (rxdv) line112 a (also shown in FIG. 11) and provides an output on the dataSelectlines 122 a-122 i to the data multiplexers 120 a-120 i in FIG. 12.

[0069] The expansion state machine 132 also provides a count enable(counten) signal on a line 140 and a count down (countdn) signal on aline 142. The count enable signal on the line 140 initiates theCollision Resolution Time indicated at 95 in FIG. 20. The count downsignal on the line 142 decrements the Collision Resolution Time on aperiodic basis to indicate at each instant the period that remains inthe Collision Resolution Time 95.

[0070] The signal on the received data valid (rxdv) line 112 a is alsointroduced to the interface logic 136. The interface logic 136 alsoreceives a drv out signal on a line 144 from the expansion state machine132. The drv out signal indicates the end of the Collision ResolutionTime. The interface logic 136 provides a plurality of outputs: (1) thedata valid (xdv) signal 60 in FIGS. 4, 7 and 20, (2) the collision(xerr) indication 70 in FIG. 20, (3) the xclk signal 92 in FIGS. 7 and20, (4) the XCOLOUT indication on the line 96 a (also shown in FIGS. 9and 11) and (5) the XCRSOUT indication 84 a (also shown in FIGS. 9 and11).

[0071] The Expansion State Machine 132 in FIG. 13 is shown in additionaldetail in FIG. 14 in the form of a flow chart or diagram. The flow chartincludes an idle block 150 which activates a WAIT_BCMI stage 152 toobtain the production of the XCRSOUT signal 90 in FIG. 20 and initiatethe production of the Collision Resolution Time indicated at 95 in FIG.20. The stage 152 then initiates the downward counting on a periodicbasis of the Collision Resolution Time 95.

[0072] During the period of the countdown, the stage 152 sends acollision signal to a COL_BCM stage 154 if a collision is indicated. Thestage 154 then sets all of the dataSelect(all) signals in FIGS. 12 to 0to provide for the operation of the multiplexers 120 a-120 i in FIG. 12in the idle state. The expansion state machine 132 then remains in theidle state during all of the time that the packet involved in thecollision is providing nibbles and thereafter until a new packet isreceived.

[0073] At the end of the Collision Resolution Time (95 in FIG. 20), theWAIT_BCMI stage provides a signal on a line 156 provided that nocollision has occurred in the time period 95 in FIG. 20. This causes theXDIR_(—)0 signal 94 in FIG. 20 to be turned on and the production of theXCLK signals 92 in FIG. 20 to be initiated. In successive ones of theXCLK signals 92, the header nibbles H1, H2, H3 and H4 are generated as aresult of the generation of the control signals dataSelect(hdr1),dataSelect(hdr2), dataSelect(hdr3) and dataSelect(hdr4) on the lines 122b, 122 c, 122 d and 122 e (also shown in FIG. 12). However, if the datavalid signal 60 (FIGS. 4, 7 and 20) is not produced in any of theseclock signals, a signal is generated on a line 158 in FIG. 14 and isintroduced to the idle stage 150 to provide for an idle operation duringthe remaining time of the packet.

[0074] An RXDV_ACTIVE state is entered in an RXDV_ACTIVE stage in FIG.14 as a result of the rxdv input control signal causing the transitionfrom HDR.3 to RXDV_ACTIVE. When no data valid signal (!rxdv) signal 60is being received and the dataSelect(trler) signal on the control line122 f (also shown in FIG. 12) is a binary 1, a SEND_FOOT1 stage 162 inFIG. 14 produces a T1 nibble. In like manner, a SEND_FOOT2 stage 164, aSEND_FOOT3 stage 166 and a SEND_FOOT4 stage 168 produce the trailernibbles T2, T3 and T4 in response to control signalsuct/dataSelect(trlr2), uct/dataSelect(trlr3), and uct/dataSelect(trlr4)control signals, (the dataSelect(trlr2), dataSelect(trlr3) anddataSelect(trlr4) control signals also being shown in FIG. 12. The “uct”in the control signals specified above indicates that the transfer isunconditional and is not dependent upon any condition. When the trailernibbles T1-T4 have been produced, the stage 150 is set to the idle stateto wait until a new packet is provided. This is provided by a uct signalon a line 169.

[0075] The data forwarding stage 108 shown in FIG. 11 as a single blockis shown in additional detail in FIG. 15. The blocks shown in FIG. 15include a start-of-frame detector (SFD) 170, a first-in-first-out (FIFO)controller 172 and a FIFO 174. The start-of-frame detector 170 receivesthe data valid (xdv) signals 60 (see also FIGS. 4, 7 and 20), the xclock(xclk) signals 92 (also shown in FIG. 20) and the xdata signals 104(also shown in FIG. 20) and produces a GOT SFD signal on a line 176.This signal indicates that the start-of-frame 16 in the packet 40 hasbeen detected. This signal activates the FIFO controller 172 whichproduces a fifoLoadenable signal on a line 178. The signal on the line178 enables the data to be loaded into the FIFO 174. The data issubsequently transferred from the FIFO 174 for the originating device 30a on the txdata line 118 a also shown in FIG. 11.

[0076]FIG. 16 shows a start-of-frame detect machine generally indicatedat 180. The state machine 180 may be considered as a part of thestart-of-frame detect stage 170 in FIG. 15. The state machine 180 may beconsidered to include an idle state 182, a GOT5 state 184 and a GOTSFDstate 186. A line 188 extending from the idle state 182 to the GOT5state 184 activates the GOT5 state when the line provides the data validsignal 60 (FIGS. 4, 7 and 20) and the xdata provides a hexadecimal valueof five (5) represented by a binary pattern of 0101.

[0077] A line 190 extending from the GOT5 state 184 to the GOTSFD state186 activates the GOT5FD state 184 when the line provides the data validsignal 60 (FIGS. 4, 7 and 20) and the xdata provides a hexadecimal valueof D (represented by a binary pattern of 1101). When this occurs, theoriginating device 30 a processes the remainder of the packet and sendsan !xdv signal on a line 192 at the end of the packet to return the SFDState Machine to the idle state 182. As previously described, the !xdvstate occurs when the data valid signal 60 (FIGS. 4, 7 and 20) is nolonger produced.

[0078] The data processor 110 in FIG. 11 is shown in additional detailin FIG. 17. The data processor 110 includes a data processing statemachine 194 and the statistics block 52. It also includes a plurality ofregisters 196 a-196 f. The data valid (xdv) signal 60 (FIGS. 4, 7 and20) and the collision (xerr) signal 70 (FIGS. 7 and 20) are introducedto the data processing state machine 194. The registers 196 a-196 c arerespectively designated as PGI1-PGI3 and the registers 196 d-196 f arerespectively designated as TRLR2-TRLR4. LoadHDR1, loadHDR2 and loadHDR3signals are respectively introduced to the registers 196 a-196 c fromthe data processing state machine 194 and loadTRLR2, loadTRLR3 andloadTRLR4 signals are respectively applied to the registers 196 d-196 f.The signals from the registers 196 a-196 f are introduced to the staticsstage 52 for recording in this stage.

[0079] Header signals for the H2 nibble are not introduced from the dataprocessing state machine 194 to a register corresponding to theregisters 196-196 c because all of the binary bits for the header nibbleH2 are 0. (See FIG. 3.) Similarly, trailer signals for the T1 nibble arenot introduced from the data processing state machine 194 to a registercorresponding to the registers 196 d-196 f because all of the binarybits for the trailer nibble T1 are 0. (See FIG. 5.)

[0080]FIG. 18 is a flow chart or diagram showing the operation of thedata processing state machine 194 in FIG. 17. As a first operation, anunconditional (uct) transfer is provided from a Save state 210 to aStart state 212. When there is a data valid (xdv) signal 60 (FIGS. 4, 7and 20), the header nibble H1 is loaded into the packet 40 as shown at214. An advance is then made to header nibble 2, as indicated at 216,when there is a data valid (xdv) signal.

[0081] Nothing is loaded in header nibble 2 because there are all binary0's in header nibble H2 (see FIG. 3). When there is a data valid (xdv)signal 60, an advance is then made to load header nibble H3 as indicatedat 218 in FIG. 18. Thereafter an advance is made, as indicated at 220,to load header nibble H4 when there is a data valid signal (xdv) 60. Ifthere is no data valid signal to load any of the data nibbles H1, H2, H3and H4, a return is made to the start state 212 as indicated at 222 inFIG. 18. A “no data” valid signal is indicated at !xdv in FIG. 18.

[0082] When there is no collision signal 70 (see FIG. 7), the trailer T1is loaded as indicated at 224. A “no collision” signal is indicated at!xerr in FIG. 18. When there is no collision signal 70 (see FIG. 4), theTrailer T2 is loaded as indicated at 226. If there is a collisionsignal, a binary “1” is produced in the trailer T2 (see the XERR columnin FIG. 8), and a return is made to the start state 210 as indicated at228 in FIG. 18. If there is not a binary “1” in the XERR column for thetrailer T2 in FIG. 8 to indicate a collision, the trailer T3 isunconditionally loaded, as indicated at 230, in accordance with the loadTRLR3 signal. Similarly, the trailer T4 is unconditionally loaded, asindicated at 232, in accordance with the load TRLR signal. When thisloading has been completed, a return is made to the Save state 210 asindicated at 232 in FIG. 18.

[0083] Although this invention has been disclosed and illustrated withreference to particular embodiments, the principles involved aresusceptible for use in numerous other embodiments which will be apparentto persons of ordinary skill in the art. The invention is, therefore, tobe limited only as indicated by the scope of the appended claims.

1. In combination for use with a plurality of originating devices and aplurality of ports on each of the originating devices in sending packetsof binary coded signals, each packet including binary coded signalsrepresenting a preamble, a start-of-frame delimiter and data, means atan individual one of the originating devices, and at an individual oneof the ports in such originating device, for receiving such packets, andmeans at the individual one of the originating devices for modifying aportion of the preamble to provide a header indicating the individualone of the originating devices and the individual one of the ports insuch individual one of the originating devices.
 2. In a combination asset forth in claim 1, means at the individual one of the originatingdevices for transmitting the header, the remaining portion of thepreamble, the start-of-frame delimiter and the data to other ones of theoriginating devices in the plurality.
 3. In a combination as set forthin claim 1, the packets being formed from successive nibbles eachdefined by a plurality of binary bits, the modifying means beingoperative to provide the last nibble in the header and the first nibblein the remaining portion of the preamble in a pattern distinguishing theheader and the remaining portion of the preamble or any two (2) nibblesof the header from the start-of-frame delimiter.
 4. In a combination asset forth in claim 1, the packet including information specifying aparticular one of the originating devices to receive the packet from theindividual one of the originating devices, and means at the particularone of the originating devices for substituting the modified portion ofthe preamble in place of the header.
 5. In a combination as set forth inclaim 4, means at the particular one of the originating devices fortransmitting the packet including the preamble, the start-of-framedelimiter and the data.
 6. In a combination as set forth in claim 1, anobserving station for receiving the packet with the header, theremaining portion of the preamble, the start-of-frame delimiter and thedata, means at the observing station for processing the header todetermine the individual one of the originating devices and theindividual one of the ports in such individual one of the originatingdevices, and means at the observing station for making a record of theindividual one of the originating devices and the individual one of theports in the individual one of the originating devices.
 7. In acombination as set forth in claim 2, the packets being formed fromsuccessive nibbles each defined by a plurality of binary bits, themodifying means being operative to provide the last nibble in the headerand the first nibble in the remaining portion of the preamble in apattern distinguishing the header and the remaining portion of thepreamble from the start-of-frame delimiter, the packet includinginformation specifying a particular one of the originating devices toreceive the packet, and means at the particular one of the originatingdevices for substituting the modified portion of the preamble in placeof the header, means at the particular one of the originating devicesfor transmitting the packet including the preamble, the start-of-framedelimiter and the data, an observing station for receiving the packetwith the header, the remaining portion of the preamble, thestart-of-frame delimiter and the data, means at the observing stationfor processing the header to determine the individual one of theoriginating devices and the individual one of the ports in suchindividual one of the originating devices, and means at the observingstation for making a record of the individual one of the originatingdevices and the individual one of the ports in the individual one of theoriginating devices.
 8. In combination at an individual one of aplurality of originating devices for receiving and processing packets ofbinary coded signals, each packet including binary coded signalsrepresenting a header, a portion of a preamble having a particularformat, a start-of-frame delimiter and data including the source of thepacket and the individual one of the originating devices as therecipient of the packet, means for receiving the packet, meansresponsive to the data indicating the individual one of the originatingdevices as the recipient of the packet for providing for a processing ofthe signal in the packets, means responsive to the header in the packetsfor substituting the particular format of the preamble for the header inthe packets, and means for transmitting the packets including thepreamble in the particular format, the start-of-frame delimiter and thedata.
 9. In a combination as set forth in claim 8 wherein the particularformat of the header constitutes a first particular format and whereinthe start-of-frame delimiter has a second format different from thefirst format and wherein the header is formed from a plurality ofnibbles each defined by a plurality of binary bits and wherein the lastnibble in the header and the first nibble in the remaining portion ofthe preamble have, a format different from the second format and whereinmeans are provided for distinguishing the last nibble in the header andthe first nibble in the remaining portion of the preamble from thestart-of-frame delimiter.
 10. In combination for use with a plurality oforiginating devices and a plurality of ports on each of the originatingdevices in sending packets of binary coded signals, each packetincluding binary coded signals representing a preamble, a starter framedelimiter and data, means at an individual one of the originatingdevices, and at an individual one of the ports in such originatingdevice, for receiving such packets, means at the individual one of theoriginating devices for modifying a portion of the preamble to provide aheader indicating the individual one of the originating devices and theindividual one of the ports in such individual one of the originatingdevices, an observing station displaced from the originating devices forreceiving the packets from the individual one of the ports in theindividual one of the originating devices, and means at the observingstation for processing the headers in the packets to determine theindividual one of the originating devices and the individual one of theports in such individual one of the originating devices.
 11. In acombination as set forth in claim 10, means at the observing station forproviding a record of the individual one of the originating devices andthe individual one of the ports in such individual one of theoriginating devices.
 12. In a combination as set forth in claim 10, thepreamble being in a particular pattern, the data including informationidentifying a particular one of the originating devices for receivingthe packets, and means at the particular one of the originating devicesfor substituting the preamble in the particular pattern for the header.13. In combination for use with an individual one of originating devicesin a plurality, and an individual one of a plurality of ports in theindividual one of the originating devices, for receiving and processingpackets of binary coded signals, each packet including, after suchprocessing a header, for identifying the individual one of theoriginating devices and the individual one of the ports in theindividual one of the originating devices, a portion of a preamblehaving a particular format, a start-of-frame delimiter and data, anobserving station displaced from the originating devices for receivingthe packets from the individual one of the ports in the individual oneof the originating devices, and a processor responsive at the observingstation to the header for determining the individual one of theoriginating devices and the individual one of the ports in theindividual one of the originating devices.
 14. In a combination as setforth in claim 13 wherein the header is formed from a plurality ofnibbles each defined by a plurality of binary bits and the remainder ofthe preamble is formed from a plurality of nibbles defined by aplurality of binary bits and wherein the last nibble in the header ischosen so that such last nibble and the remaining portion of thepreamble have a format different from any two (2) nibbles in the headerand wherein means are provided at the observing station fordistinguishing the last nibble in the header and the first nibble in theremaining portion of the preamble from any two (2) nibbles in theheader.
 15. A method of indicating an individual one of a plurality oforiginating devices, and an individual one of the ports in suchindividual one of the originating devices, for receiving packets ofbinary coded signals from an external source, each of the packets beingformed from a plurality of nibbles and including a preamble, astart-of-frame delimiter and data, including the steps of: receiving thepackets from the external source at the individual one of the ports inthe individual one of the originating devices, substituting, for aportion of the preamble as represented by a particular number of thenibbles in the preamble, a header indicating the individual one of theoriginating device and indicating the individual one of the ports in theindividual one of the originating devices, and transmitting the packetwith the header, the remaining portion of the preamble, thestart-of-frame delimiter, and the data to the other originating devicesin the plurality.
 16. A method as set forth in claim 15 wherein one ofthe originating devices in the plurality other than the individual oneof the originating devices substitutes the preamble for the header inthe transmitted packets and transmits the packets with the preamble, thestart-of-frame delimiter and the data.
 17. A method as set forth inclaim 15 including the steps of: transmitting the packet with theheader, the remaining portion of the preamble, the start-of-framedelimiter and the data to an observing station, determining at theobserving station from the header the individual one of the originatingdevices in the plurality and the individual one of the ports in theindividual one of the originating devices, and recording at theobserving station the individual one of the originating devices and theindividual one of the ports in the individual one of the originatingdevices.
 18. A method as set forth in claim 16, including the steps of:transmitting the packet with the header, the remaining portion of thepreamble, the start-of-frame delimiter and the data to an observingstation, determining at the observing station from the header theindividual one of the originating devices in the plurality and theindividual one of the ports in the individual one of the originatingdevices, and recording at the observing station the individual one ofthe originating devices and the individual one of the ports in theindividual one of the originating devices.
 19. A method of indicating anindividual one of a plurality of originating devices, and an individualone of a plurality of ports in such individual one of the originatingdevices, for receiving packets of signals from an external source, eachof the packets being formed from a plurality of nibbles and including aheader, the remaining portion of a preamble, a start-of-frame delimiterand data, the header indicating the individual one of the plurality oforiginating devices and indicating the individual one of the ports inthe individual one of the indicating devices, including the steps of:receiving the packets at an observing station, processing at theobserving station the headers in the packets to determine the individualone of the originating devices and the individual one of the ports inthe individual one of the originating devices, and making a record ofthe individual one of the originating devices and the individual one ofthe ports in the individual one of the originating devices.
 20. A methodas set forth in claim 19, including the steps of: receiving the packetsat other ones of the originating devices in the plurality, andconverting the headers in the packets at such other ones of theoriginating devices in the plurality to the preamble.
 21. A method asset forth in claim 20, including the steps of: the preamble being formedfrom a plurality of nibbles each having a particular pattern, the headerbeing formed from a plurality of nibbles, the conversion of the nibblesin the header at such other ones of the originating devices to thepreamble being In the particular pattern.
 22. A method of indicating anindividual one of a plurality of originating devices, and an individualone of a plurality of ports in such individual one of the originatingdevices, for receiving packets of binary coded signals from an externalsource, each of the packets being formed from a plurality of nibbles andincluding a header, the remaining portion of a preamble, astart-of-frame delimiter and data, the header indicating the individualone of the plurality of originating devices and indicating theindividual one of the ports in the individual one of the indicatingdevices, including the steps of: receiving the packets at other ones ofthe originating devices in the plurality, and converting the headers inthe packets at such other ones of the originating devices in theplurality to the preamble.
 23. A method as set forth in claim 22,including the steps of: the preamble being formed from a plurality ofnibbles each having a particular pattern, the header being formed from aplurality of nibbles, the conversion of the nibbles in the header atsuch other ones of the originating devices to the preamble being in theparticular pattern.
 24. In combination for use with a plurality oforiginating devices and a plurality of ports on each of the originatingdevices in sending packets of binary coded signals to other originatingdevices in the plurality, each packet including binary coded signalsrepresenting a preamble, a start-of-frame delimiter and data, a senderin each of the originating devices for sending packets from suchoriginating device to other originating devices in the plurality, meansin each of the originating devices for providing a trailer at the end ofeach packet, and an encoder in each of the originating devices forindicating in the trailer in each packet from such originating devicewhether or not such originating device has experienced a collision inthe sending of such packet from such originating device with the sendingof a packet from another of the originating devices in the plurality.25. In a combination as set forth in claim 24 wherein the encoder ineach of the originating devices is operative to indicate in the trailerfrom such originating device whether or not each packet from suchoriginating device is a normal packet.
 26. In a combination as set forthin claim 24 wherein the encoder in each of the originating devices isoperative to indicate in the trailer from such originating devicewhether or not such packet is from an acceptable source.
 27. In acombination as set forth in claim 24 wherein the encoder in each of theoriginating devices is operative to indicate in each of the trailersfrom such originating device the space between the end of such packetand the beginning of the next packet.
 28. In a combination as set forthin claim 24, an observing station for receiving the packets with thepreamble, the start-of-frame limiter, the data and the trailer, aprocessor in the observing station for processing the trailer in eachpacket from such originating device to determine if a collision isindicated in such trailer between the sending of such packet from suchoriginating device and a simultaneous sending of a packet from anotherone of the indicating devices, and a recorder for recording theoccurrence of collisions in the processed trailers from such originatingdevice.
 29. In a combination as set forth in claim 24, the encoder ineach of the originating devices being operative to indicate in thetrailer for each packet from such originating device whether or not suchpacket from such originating device is a normal packet, an observingstation for receiving the packets with the preamble, the start-of-framelimiter, the data and the trailer, a processor in the observing stationfor processing the trailer in each packet from such originating deviceto determine if such packet is a normal packet, and a recorder forrecording, in accordance with the processing of the trailer in eachpacket from such originating device, whether or not such packet isnormal.
 30. In a combination as set forth in claim 24, each packet beingdefined by a plurality of successive nibbles, the encoder in each of theoriginating devices being operative to indicate in the trailer for eachpacket from such originating device whether or not such packet from suchoriginating device is a runt packet having a number of nibbles less thana particular number, an observing station for receiving the packets withthe preamble, the start-of-frame limiter, the data and the trailer, aprocessor in the observing station for processing the trailer in eachpacket to determine if such packet is a runt packet, and a recorder forrecording, in accordance with the processing of the trailer in eachpacket from such originating device, whether or not such packet is arunt packet.
 31. In a combination as set forth in claim 24, the encoderin each of the originating devices being operative to indicate in thetrailer for each packet from such originating device whether or not suchpacket is from an acceptable source, an observing station for receivingthe packet with the preamble, the start-of-frame limiter, the data andthe trailer, a processor in the observing station for processing thetrailer in each packet from such originating device to determine if thepacket contains a start-of-frame delimiter, and a recorder forrecording, in accordance with the processing of the trailer in eachpacket from such originating device, whether or not the packet containsa start-of-frame delimiter.
 32. In a combination as set forth in claim24, the encoder in each of the originating devices being operative toindicate, in the trailer for each packet form such originating device,the space between the end of each packet and the beginning of the nextpacket, an observing station for receiving the packet with the preamble,the start-of-frame limiter, the data and the trailer, a processor in theobserving station for processing the trailer in such packet from suchoriginating device to determine the space between the end of such packetand the beginning of the next packet, and a recorder for recording, inaccordance with the processing of the trailer in each packet from suchoriginating device, the space between the end of such packet and thebeginning of the next packet.
 33. In a combination as set forth in claim1, each packet also including a trailer at the end of the packet, thetrailer in each packet providing an indication of whether or not acollision has occurred between the sending of such packet by theindividual one of the originating devices and the simultaneous sendingof another packet by one of the originating devices other than theindividual one of the originating devices, and means for processing thetrailer in each packet from such individual one of the originatingdevices to determine whether or not a collision has occurred between thesending of such packet by the individual one of the sending devices andthe simultaneous sending of another packet by one of the originatingdevices other than the individual one of the originating devices.
 34. Ina combination as set forth in claim 6, each packet also including atrailer at the end of the packet, the trailer in each packet providingan indication of whether or not a collision has occurred between thesending of such packet by the individual one of the originating devicesand the simultaneous sending of another packet by one of the originatingdevices other than the individual one of the originating devices, andmeans for processing the trailer to determine whether or not a collisionhas occurred between the sending of such packet by the individual one ofthe originating devices and the simultaneous sending of another packetby one of the originating devices other than the individual one of theoriginating devices.
 35. In a combination as set forth in claim 33, thetrailer in each packet providing an indication of at least one of thefollowing: (a) whether or not such packet is a normal packet, (b)whether or not such packet is a runt packet, (c) whether or not suchpacket is from an acceptable source, (d) whether or not such packetincludes a start-of-frame delimiter and (e) the space between the end ofsuch packet and the beginning of the next packet from such individualone of the originating devices, and means for processing the trailer ineach packet from the individual one of the originating devices todetermine at least one of the following: (a) whether or not such packetis a normal packet, (b) whether or not such packet is a runt packet, (c)whether or not such packet is from an acceptable source, (d) whether ornot such packet includes a start-of-frame delimiter and (e) the spacebetween the end of each packet and the beginning of the next packet fromsuch individual one of the originating devices.
 36. In a combination asset forth in claim 34, the trailer in each packet providing anindication of at least one of the following: (a) whether or not suchpacket is a normal packet, (b) whether or not such packet is a runtpacket, (c) whether or not such packet is from an acceptable source, (d)whether or not such packet includes a start-of-frame delimiter and (e)the space between the end of each packet and the beginning of the nextpacket from such individual one of the originating devices, means forprocessing the trailer to determine at least one of the following: (a)whether or not such packet-is a normal packet, (b) whether or not suchpacket is a runt packet, (c) whether or not such packet is from anacceptable source, (d) whether or not such packet includes astart-of-frame delimiter and (e) the space between the end of eachpacket and the beginning of the next packet from such individual one ofthe originating devices.
 37. In a combination as set forth in claim 10,each packet including a trailer at the end of the packet, the trailer ineach packet providing an indication of whether or not a collision hasoccurred between the sending of such packet by the individual one of theoriginating devices and the simultaneous sending of another packet byone of the originating devices other than the individual one of theoriginating devices; means for processing the trailer in each packet todetermine whether or not a collision has occurred between the sending ofsuch packet by the individual one of the originating devices and thesimultaneous sending of another packet by one of the originating devicesother than the individual one of the originating devices.
 38. In acombination as set forth in claim 37, means at the observing station forproviding a recording of the determination provided by the processing ofthe trailer in each packet.
 39. In a combination as recited in claim 14,each packet including a trailer at the end of the packet, the trailer ineach packet providing an indication of whether or not a collision hasoccurred between the sending of such packet by the individual one of theoriginating devices and the simultaneous sending of another packet byone of the originating devices other than the individual one of theoriginating devices; means for processing the trailer in each packet todetermine whether or not a collision has occurred between the sending ofsuch packet by the individual one of the originating devices and thesimultaneous sending of another packet by one of the originating devicesother than the individual one of the originating devices.
 40. In acombination as set forth in claim 39, means at the observing station forproviding a recording of the determination provided by the processing ofthe trailer in each packet.
 41. In a combination as set forth in claim39, the trailer in each packet providing an indication of at least oneof the following: (a) whether or not such packet is a normal packet, (b)whether or not such packet is a runt packet, (c) whether or not suchpacket is from an acceptable source, (d) whether or not such packetincludes a start-of-frame delimiter and (e) the space between the end ofsuch packet and the beginning of the next packet from such individualone of the originating devices, and means for processing the trailer ineach packet from the individual one of the originating devices todetermine at least one of the following: (a) whether or not such packetis a normal packet, (b) whether or not such packet is a runt packet, (c)whether or not such packet is from an acceptable source, (d) whether ornot such packet includes a start-of-frame delimiter and (e) the spacebetween the end of each packet and the beginning of the next packet fromsuch individual one of the originating devices.
 42. In a combination asset forth in claim 40, the trailer in each packet providing anindication of at least one of the following: (a) whether or not suchpacket is a normal packet, (b) whether or not such packet is a runtpacket, (c) whether or not such packet is from an acceptable source, (d)whether or not such packet includes a start-of-frame delimiter and (e)the space between the end of each packet and the beginning of the nextpacket from such individual one of the originating devices, and meansfor processing the trailer to determine at least one of the following:(a) whether or not such packet is a normal packet, (b) whether or notsuch packet is a runt packet, (c) whether or not such packet is from anacceptable source, (d) whether or not such packet includes astart-of-frame delimiter and (e) the space between the end of eachpacket and the beginning of the next packet from such individual one ofthe originating devices.
 43. A method as set forth in claim 17,including the steps of: each packet also including a trailer at the endof the packet, the trailer in each packet providing an indication ofwhether or not a collision has occurred between the sending of suchpacket by the individual one of the originating devices and thesimultaneous sending of another packet by one of the originating devicesother than the individual one of the originating devices, and processingthe trailer in each packet from such individual one of the originatingdevices to determine whether or not a collision has occurred between thesending of such packet by the individual one of the sending devices andthe simultaneous sending of another packet by one of the originatingdevices other than the individual one of the originating devices.
 44. Amethod as set forth in claim 43, including the step of: the trailer ineach packet providing an indication of at least one of the following:(a) whether or not such packet is a normal packet, (b) whether or notsuch packet is a runt packet, (c) whether or not such packet is from anacceptable source, (d) whether or not such packet includes astart-of-frame delimiter and (e) the space between the end of eachpacket and the beginning of the next packet from such individual one ofthe originating devices, processing the trailer in each packet from theindividual one of the originating devices to determine at least one ofthe following: (a) whether or not such packet is a normal packet, (b)whether or not such packet is a runt packet, (c) whether or not suchpacket is from an acceptable source, (d) whether or not such packetincludes a start-of-frame delimiter and (e) the space between the end ofeach packet and the beginning of the next packet from such individualone of the originating devices.